The present invention relates generally to chimeric polypeptides containing chemokine polypeptide domains. More specifically, the invention relates to the expression in host cells of recombinant polynucleotide sequences encoding chemokine polypeptides covalently attached to heterologous polypeptides, and the use of such chimeric polypeptides as research tools for identifying chemokine receptors, as vaccine adjuvants, as agents-for the chemotactic recruitment of migratory cells, as agents for the stimulation or inhibition of angiogenesis, as agents against autoimmune diseases and inflammation, and as agents to inhibit the binding of HIV to certain receptors.
Chemokines (or chemotactic cytokines) are a class of cytokine molecules capable of chemotactically attracting migratory cells, and are involved in cell recruitment and activation in inflammation. Chemokines generally have small molecular weights in the range of 8-10 kDa and, like other small proteins such as cytokines, are believed to be rapidly inactivated in vivo, resulting in relatively short biological half-lives for these proteins. Most chemokines can be divided into two subgroups, CXC or CC, on the basis of the spacing of two highly-conserved cysteine amino acids near the amino terminus of these proteins. Within the CXC and CC subgroups, chemokines are further grouped into related families based on amino acid sequence similarity between them. CXC chemokine families include the IP-10 and Mig family; the GROα, GROβ, and GROγ family; the interleukin-8 (IL-8) family; and the PF4 family. CC chemokine families include the monocyte chemoattractant protein (MCP) family; the family including macrophage inhibitory protein-1α (MIP-1α), macrophage inhibitory protein-1β (MIP-1β), and regulated on activation normal T cell expressed (RANTES); and the lymphotactin family. The chemokines stromal cell-derived factor 1α (SDF-1α) and stromal cell-derived factor 1β (SDF-1β) form a chemokine family that is approximately equally related by amino acid sequence similarity to the CXC and CC chemokine subgroups. Individual members of the chemokine families are known to be bound by at least one chemokine receptor, with CXC chemokines generally bound by members of the CXCR class of receptors, and CC chemokines by members of the CCR class of receptors. For example, SDF-1α is known to be a ligand for the CXCR receptor fusin/CXCR4, and MIP-1α is bound by the CCR receptors CCR1, CCR4, and CCR5.
The presence of a chemokine gradient attracts migratory cells such as lymphocytes, leukocytes, and antigen-presenting cells (APCs) that may participate in autoimmune reactions, inflammation, or normal immune responses, or that may release other intercellular factors to stimulate or inhibit angiogenesis or other cellular processes. For example, the initiation of autoimmune disease requires the infiltration or recruitment of lymphocytes able to respond against self proteins into the organ bearing the antigenic self proteins. Inflammatory atherosclerotic lesions are due in part to infiltration of the vascular compartment by leukocytes recruited to the site. To induce an immune response, antigenic proteins and glycoproteins must bind to the surface of B lymphocytes to stimulate antibody production, and must be taken up by antigen-presenting cells, processed, and represented to T lymphocytes to mediate a T-lymphocyte response. Migratory cells that secrete IP10 or IL-8, when attracted by a chemokine gradient to a particular site, respectively may inhibit or stimulate the formation of blood vessels at that site. Chemokines may be used to establish a chemoattractive gradient for migratory cells that are expressing the appropriate chemokine receptors, or to obscure an existing chemoattractive gradient.
Chemokine receptors are also involved in functions other than chemotaxis, such as interacting with viral proteins. HIV-1 is known to bind to certain proteins on the surface of cells in order to gain entrance into these cells and replicate or integrate the viral gene into the host DNA. The CD4 protein on T lymphocytes and other cells, including certain antigen presenting cells, has been shown to be bound by the HIV-1 viral envelope protein gp120. This is believed to induce in gp120 a conformational change that then exposes regions of gp120 and perhaps CD4 that subsequently bind to a chemokine receptor. To date CXCR4 (also known as fusin), CCR5, and several other chemokine receptors have been identified as co-receptors for HIV-1. Monocyte-tropic (M-tropic) isolates of HIV-1 require interaction with CCR5 in order to infect cells, while T-lymphocyte-tropic (T-tropic) HIV-1 isolates require another coreceptor, CXCR4, for infection. There is some evidence indicating that HIV-1 can also use other CCR receptors such as CCR2 and CCR3 to gain entry into cells expressing them. For some HIV-2 isolates, it appears that certain chemokine receptors such as fusin/CXCR4 alone can provide the cell-surface protein needed for binding and entrance into the cell.
HIV-1 infection of cells expressing CD4 and fusin/CXCR4 is greatly decreased by the addition of purified SDF-1α, which is bound by fusin/CXCR4. We have found that preincubation of cells in the presence of purified SDF-1α for a short period of time at 37° C. causes a profound down-regulation of the receptor. This down-regulation of fusin/CXCR4 correlates with a decrease in the ability of HIV-1 to infect cells.
There is a continuing requirement for new compositions that will enhance, alter, or inhibit the effects of chemokine-receptor interactions, and for methods for their use.